Hydrotropic process for green biorefinery applications

Biorefinery is a concept of sustainable biomass processing into several useful products, such as fuels, materials, power and chemicals. The necessity of more extensive biomass utilization is governed nowadays by the intensively growing population and the increased pollution caused by the usage of oilbased products, which lead, among other things, to the global climate change. However, successful implementation of the biorefinery concept requires efficient fractionation technologies. Therefore, the aim of the present studywas the investigation of a hydrotropic process as a method for biomass fractionation. The hydrotropic method is an environmentally friendly waterbased process that possesses several attractive features, such as simple recovery of the hydrotropic solution and possibility to obtain, besides fibers, several by-products.

In the scope of the study, two raw materials, namely birch wood chips from Finland and sugarcane bagasse from Brazil, were treated with the hydrotropic method, and the obtained fractions were characterizedemploying different techniques. In addition, lignin hydrotropically extracted from birch wood was utilized for the preparation of lignin-cellulose particles.

The result of the fractionation of the birch wood chips showed that this raw material could be efficiently delignified with the process under the conditions employed. The modification of the solutions with formic acid, or hydrogen peroxide, or both improved considerably the delignification efficiency. Generally, the produced pulps were enriched in cellulose. Subsequent bleaching further increased the cellulose content. Therefore, the obtained cellulose fractions could potentially be used as dissolving grade pulps. Lignins extracted from the wood by the unmodified and modified (formic acid and hydrogen peroxide) hydrotropic solutions were isolated by dilution of the spent solutions with water and filtration and had low contents of non-lignin compounds.

Sugarcane bagasse was fractionated with a hydrotropic process at different treatment temperatures and times. Generally, two fractions, namely cellulose and lignin, were obtained. The purity of both fractions and the yield of lignin were higher at more severe treatment conditions. The spent solutions from the treatments contained, besides lignin, also dissolved hemicelluloses, sugar monomers, furfural, acetic and formic acids. The content of the dissolved components varied depending on the treatment conditions.

Lignin extracted from birch wood with a conventional hydrotropic method was mixed with cellulose and shaped into beads employing 7% NaOH/12% urea aqueous solution as a solvent. The beads in the never-dried state were highly porous particles, and the lignin was evenly distributed in them. Antibacterial studies against the common pathogens Staphylococcus aureus and Escherichia coli revealed that the beads could inhibit the growth of S. aureus, and the extent of the inhibition correlated with the lignin content in the beads.

The results summarized in the thesis showed a great potential of the hydrotropic treatment for fractionation of hardwood and non-wood raw materials into valuable products, such as cellulose and lignin. Positive aspects of the hydrotropic treatment with the respect to the recovery of the named fractions are simple isolation of the extracted lignin from the solution and minimal losses of cellulose over the course of the treatment. In addition, both fractions can be produced with a high degree of purity, and they present excellent raw materials for further conversion. As was shown with sugarcane bagasse, besides the main streams, several other products (furfural and acetic acid) can be obtained as well. Overall, the results of the thesis can serve as a basis for further development of hydrotropic process-based biorefinery technology.